Patent Application
20100217247
The present invention pertains generally to ophthalmic surgery. More particularly, the present invention pertains to systems and methods for correcting visual aberrations that are introduced into an eye during a laser surgery operation. The present invention is particularly, but not exclusively, useful as a system and method for using Laser Induced Optical Breakdown (LIOB) to weaken stromal tissue, and thereby correct visual aberrations that are introduced by the photoablation (removal) of corneal tissue during a surgical procedure.
Laser surgery that is performed on the cornea of an eye to correct a vision defect is typically accomplished in either of two different ways. For one, tissue can be removed from the cornea by photoablation to reshape the eye. Examples of such a surgical operation are the familiar PRK and LASIK procedures. Apart from photoablation, a more recently established surgical operation involves only the weakening of tissue rather than its removal. More specifically, this weakening of the cornea is done by cutting tissue in predetermined patterns inside the stroma of the cornea by a process known as Laser Induced Optical Breakdown (LIOB). The result is a redistribution of biomechanical stresses in the weakened stromal tissue that responds to intraocular pressure, to thereby reshape the cornea for correction of the vision defect.
Of the two different types of operations mentioned above, the removal of tissue by photoablation is able to accomplish more extensive corrections (i.e. provide greater diopter changes), than is possible with the second type operation wherein stromal tissue is only weakened by LIOB. Although photoablation may be required for the more extensive refraction corrections, or may otherwise be preferable, photoablation is known to sometimes introduce unwanted visual aberrations. More specifically, as an eye stabilizes after the surgical removal of tissue (i.e. photoablation), the eye can reshape in an unpredicted way that will introduce these unwanted aberrations.
Whenever corneal tissue is removed (i.e. photoablated) from the eye, it is essential that a sufficient amount of tissue remain. Obviously, there are limits to how much tissue can be actually removed. Further, the visual aberrations noted above, and particularly the higher order aberration, can be very detrimental or extremely annoying if left uncorrected. Unfortunately, it can happen that the introduced aberrations are not manifest until weeks after the initial corrective surgery.
In light of the above, it is an object of the present invention to provide a system and method for refining a laser surgical operation to correct for visual aberrations that may be introduced during a primary surgical operation. Still another object of the present invention is to provide a system and method for removing or minimizing visual aberrations, and particularly higher order aberrations, that may be introduced as an eye stabilizes after a surgical laser operation. Yet another object of the present invention is to provide a system and method for eliminating or minimizing surgically introduced visual aberrations that are simple to implement, are easy to use and are comparatively cost effective.
In accordance with the present invention, an eye is evaluated after it has been subjected to a laser surgical operation for the correction of a vision defect. Specifically, the eye is evaluated after the operation to determine whether any visual aberrations were somehow inadvertently introduced into the eye during the surgical operation. If so, it is envisioned that the newly introduced aberrations will be corrected by selectively weakening stromal tissue. For the present invention this is to be done by the process of Laser Induced Optical Breakdown (LIOB). Further, as recognized by the present invention, this subsequent correction by LIOB may be most appropriate when the primary surgical operation has involved the removal of corneal tissue by photoablation (e.g. PRK or LASIK).
It often happens that visual aberrations, including higher order aberrations, are introduced into an eye as a result of a surgical procedure. Of particular interest here are the unpredicted aberrations that are caused by the removal (i.e. photoablation) of tissue during a primary surgical procedure. In some instances, these aberrations may be immediately detectable. On the other hand, as is more often the case, they do not fully manifest themselves until sometime after the initial surgery. This can be as much as two weeks, or more. In any event, it may either be undesirable or impossible to remove (photoablate) additional tissue to correct any aberrations that may have been surgically introduced. On the other hand, LIOB may still be possible as it essentially requires no additional removal of tissue. Furthermore, LIOB is known to be effective for correcting all orders of aberrations.
As envisioned for the present invention, a system for minimizing optical aberrations that may be introduced into an eye during laser surgery includes a first laser unit (e.g. an excimer laser). This first laser unit actually performs the laser surgery by ablating corneal tissue to achieve a predetermined refractive correction. After the laser surgery (photoablation) has been completed, the eye is then evaluated to detect any aberrations that may have been introduced into the eye by the first laser unit. If such aberrations are present, a second laser unit (e.g. a pulsed femtosecond laser) is used to cause Laser Induced Optical Breakdown (LIOB) on intrastromal tissue of the eye. The consequence here is a redistribution of biomechanical stresses in the stroma that, in response to intraocular pressure in the eye, will reshape the cornea to minimize the aberrations introduced by the earlier photoablation.
It is to be appreciated that the aberrations introduced by the first laser unit may be higher order aberrations. If so, the higher order aberrations are identified with reference to at least one offset axis, wherein the offset axis is substantially parallel to the visual axis of the eye. The second laser unit is then used to weaken stromal tissue by LIOB with reference to the offset axis to correct the higher order aberrations.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Referring initially to
Still referring to
In
Block 34 indicates that the eye 20 may need some time to stabilize after the photoablation contemplated by block 32. Although no stabilization time may be required for some procedures, it can happen that as much as two weeks, or more, may be required for the results of photoablation to properly stabilize. In any event, as indicated by the block 36 in the methodology 30, after the eye 20 has stabilized, it is evaluated for aberrations that may have been introduced during the task shown in block 32. As envisioned for the present invention, and by way of example, this evaluation may detect higher order aberrations, such as astigmatism, coma or trefoil. Regardless of the type or order of these aberrations, they should be somehow minimized. As indicated in block 38 of the methodology 30, the present invention envisions minimizing introduced aberrations by performing LIOB on the cornea 18.
Although symmetrical and asymmetrical aberrations of different orders may be introduced during a primary laser procedure (block 32), block 38 indicates that LIOB as a corrective surgical procedure is appropriate in all cases. In particular, the present invention anticipates the higher order aberrations that require refractive corrections offset from the visual axis 24. With reference to
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While the particular System and Methods for Minimizing Higher Order Aberrations Introduced During Refractive Surgery as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
